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.TH PTHREAD_RWLOCK_WRLOCK 3C "Mar 23, 2005"
.SH NAME
pthread_rwlock_wrlock, pthread_rwlock_trywrlock \- lock or attempt to lock
read-write lock object for writing
.SH SYNOPSIS
.LP
.nf
cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
#include <pthread.h>

\fBint\fR \fBpthread_rwlock_wrlock\fR(\fBpthread_rwlock_t\fR \fI*rwlock\fR);
.fi

.LP
.nf
\fBint\fR \fBpthread_rwlock_trywrlock\fR(\fBpthread_rwlock_t\fR \fI*rwlock\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBpthread_rwlock_wrlock()\fR function applies a write lock to the
read-write lock referenced by \fIrwlock\fR. The calling thread acquires the
write lock if no other thread (reader or writer) holds the read-write lock
\fIrwlock\fR. Otherwise, the thread blocks until it can acquire the lock.
.sp
.LP
The \fBpthread_rwlock_trywrlock()\fR function applies a write lock like the
\fBpthread_rwlock_wrlock()\fR function, with the exception that the function
fails if any thread currently holds \fIrwlock\fR (for reading or writing).
.sp
.LP
Writers are favored over readers of the same priority to avoid writer
starvation. See \fBpthread_rwlock_rdlock\fR(3C).
.sp
.LP
Results are undefined if any of these functions are called with an
uninitialized read-write lock.
.sp
.LP
If a signal is delivered to a thread waiting for a read-write lock for writing,
upon return from the signal handler the thread resumes waiting for the
read-write lock for writing as if it was not interrupted.
.SH RETURN VALUES
.sp
.LP
If successful, the \fBpthread_rwlock_wrlock()\fR function returns \fB0\fR.
Otherwise, an error number is returned to indicate the error.
.sp
.LP
The \fBpthread_rwlock_trywrlock()\fR function returns \fB0\fR if the lock for
writing on the read-write lock object referenced by \fIrwlock\fR is acquired.
Otherwise an error number is returned to indicate the error.
.SH ERRORS
.sp
.LP
The \fBpthread_rwlock_wrlock()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEDEADLK\fR\fR
.ad
.RS 11n
The current thread already owns the read-write lock for writing or reading.
.RE

.sp
.LP
The \fBpthread_rwlock_trywrlock()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEBUSY\fR\fR
.ad
.RS 9n
The read-write lock could not be acquired for writing because it was already
locked for reading or writing.
.RE

.SH ATTRIBUTES
.sp
.LP
See  \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR pthread_rwlock_init (3C),
.BR pthread_rwlock_rdlock (3C),
.BR pthread_rwlock_unlock (3C),
.BR pthread_rwlockattr_init (3C),
.BR attributes (7),
.BR standards (7)
